FAQs for Newbies

Most of what follows here are some background FAQs about fusion and the Farnsworth Fusion project conducted under the auspices of ITT in Fort Wayne, Indiana in the 1960s.

For more specific information about building and operating a Fusor, go to

The FAQs

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The subject of controlled nuclear fusion is both amazingly simple in it’s concept and incredibly complex in its execution.  If you are completely new to the topic, then the questions and answers here will help you get a basic grasp of some of the basic issues, and familiarize you with some of the results of the earliest experiments with this technology (fifty years ago!):

Q. What are the by-products of a fusion reactor?
A: The combination of hydrogen atoms produces helium, an inert gas; the mass of the helium atoms being less than the mass of the combinant hydrogren atoms, the difference is given off as energy according to Einstein’s famous formual E=MC2. The energy is transferred to neutrons which are thrown out of the reaction at different rates, and also protons. There is also some tritium produced, which has radioactive half life of twelve years.
Q: I wonder why radiation concerns are not mentioned in published articles about the period when when ITT and Dr. F were working together. The pictures show no radiation suits on the experimentors, no gadgetry around which would be related to that.
A: These people had a special shielded “cave” to work in. The most productive fusors were also tested in a shielded “pit.” No radiation suits were needed because the tests were run at relatively low power levels, and the personnel was isolated from the Device Under Test by either the “cave” or the “pit.”
Q: What does the fusor use for fuel? A: Fusors usually run on deuterium gas. More advanced experiments can use tritium, which is a radioactive isotope of hydrogen. As such tritium is highly regulated an unavailable for unsanctioned fusion experiments. In the future a fusor could run on He3 or Boron.
Q: How did they solve the problem of introducing new fuel into the chamber?A: They didn’t, really, so far as we know, although there are some tantalizing stories about ” startling and unexplained” events in the Fusor lab that suggest the problem may have solved itself on undocumented occasions. 
Q: I thought temps in the 100,000,000-degree range were required to cause fusion, how did DR. F manage this with less?
A: Actually, the plasma within the fusor can reach at temperatures in the 20- 400 million degree range, depending on the fuel used. That such temperatures can be reached, and sustained for periods of several minutes, without destroying the fusor vessel is the magic of the “poissor,” Farnsworth’s name for the sheath of electrostatic shields that form within the fusor.
Q:Why didn’t BYU continue his work after Farnsworth passed away?
A: Philo Farnsworth left ITT and relocated to Salt Lake in 1967 with the intention of continuing his fusion research, but a series of unfortunate business decisions conspired against his work and, ultimately, his life. At least one operative Fusor was given to BYU, but students and professors there could not continue work without Dr. Farnsworth hinmself. Farnsworth was a unique individual, a gifted scientist endowed with special insights into the inner workings of the atom – insights that he was at times unable to convey to his colleagues. a special man . Without his guidance the work ground to a halt.
Q: Do you need a patent to build one of these things?
A: The ITT Corporation suspended all work on fusors in 1968, after the Atomic Energy Commission’s fusion department refused to provide any funding. The patents that Philo Farnsworth while employed by ITT expired in the mid-1980s, and are now part of the public domain, but the patents are regarded as “incomplete” and do not disclose a fully functional (i.e. net-energy generating) fusion device.
Likewise, the patent for the “Hirsch-Meeks” variation of the Farnsworth Fusor, which is the Fusor that the members of this site are experimenting with, also expired in the mid-1980s. Patents are granted for a non-renewable, 17-year term, after which the art disclosed therein enters the public domain. The Hirsch-Meeks patent was issued in 1968, and so would have expired in 1985. Consequently, none of the art being experimented with here is under any patent authority.
Q: Why can’t I find anything in the library about this subject ?
A: There really is just not very much material available anywhere on the subject of inertial electrostatic confinement fusion. Most of the writing on the subject has focused on the magnetic confinement schemes, primarily a breed of machine called the “Tokamak” which sponged up the majority of the interest and funding for fusion research for the last 35 years. You might try looking for a book called “Fusion – The Search for Endless Energy” by Robin Herman. Try an out of print bookseller like Alibris.com
Q: Why is neutron flux dangerous ?
A: Humans are in large proportion plain old water. If a neutron encounters and sticks to an ordinary water molecule it forms deuterium and releases a burst of gamma rays that causes genetic mutation and sometimes cell death. A neutron flux is more than one neutron. The larger the number of neutrons that hit you the more damage is done. A flux greater than 10e12 is a fatal exposure in the long term. A flux in the 10e13 range is a death in a week. If you want an accurate representation of what transmurasion (radiation) sickness looks like rent the movie Fat Man and Little Boy with John Cusak and Paul Newman. A naked core accident is portrayed in vivid detail…… not for kids. An accident like that is in the 10^20 neutron range. (Answer by Larry Liens)
Q. What is “Star Mode” ?
photo: Brian McDermott

A: This question was submitted by Alex Sloat (07/11/2002). We turn to Richard Hull for the definitive answer and an illustration from his own fusor:This is a visual signature of good clean operation of a fusor. It heralds a major, initial success in the construction of the basic device.In the fusor, good geometrical alignment of the inner grid structure is important. A clean vacuum that is free of organic vapor and, hopefully, water vapor is also desired. If these criteria are met, then the indicative visual signature is referred to as “star mode”. The appearance to the eye is of a glowing ball of plasma within the center of the inner grid with what appears to be multiple radiating, fine pencil like rays streaming out of it through virtually every opening in the inner grid. It is not only unmistakable and beautiful but shows that most of the basic hurdles in fusor operation have been conquered.This mode of operation is a virtual “must have” in a demo fusor before moving on to a real neutron producing fusor with deuterium gas atmosphere.

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